<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Relation of V4L2 to other Linux multimedia APIs</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REL="HOME"
TITLE="Video for Linux Two API Specification"
HREF="book1.htm"><LINK
REL="UP"
TITLE="Changes"
HREF="c14595.htm"><LINK
REL="PREVIOUS"
TITLE="Changes of the V4L2 API"
HREF="x15446.htm"><LINK
REL="NEXT"
TITLE="Experimental API Elements"
HREF="x16453.htm"></HEAD
><BODY
CLASS="SECTION"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>Video for Linux Two API Specification: Revision 0.24</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="x15446.htm"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 6. Changes</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="x16453.htm"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECTION"
><H1
CLASS="SECTION"
><A
NAME="OTHER"
>6.3. Relation of V4L2 to other Linux multimedia APIs</A
></H1
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="XVIDEO"
>6.3.1. X Video Extension</A
></H2
><P
>The X Video Extension (abbreviated XVideo or just Xv) is
an extension of the X Window system, implemented for example by the
XFree86 project. Its scope is similar to V4L2, an API to video capture
and output devices for X clients. Xv allows applications to display
live video in a window, send window contents to a TV output, and
capture or output still images in XPixmaps<A
NAME="AEN16435"
HREF="x16430.htm#FTN.AEN16435"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
>. With their implementation XFree86 makes the
extension available across many operating systems and
architectures.</P
><P
>Because the driver is embedded into the X server Xv has a
number of advantages over the V4L2 <A
HREF="x6570.htm"
>video
overlay interface</A
>. The driver can easily determine the overlay
target, i.&nbsp;e. visible graphics memory or off-screen buffers for a
destructive overlay. It can program the RAMDAC for a non-destructive
overlay, scaling or color-keying, or the clipping functions of the
video capture hardware, always in sync with drawing operations or
windows moving or changing their stacking order.</P
><P
>To combine the advantages of Xv and V4L a special Xv
driver exists in XFree86 and XOrg, just programming any overlay capable
Video4Linux device it finds. To enable it
<TT
CLASS="FILENAME"
>/etc/X11/XF86Config</TT
> must contain these lines:</P
><P
><PRE
CLASS="SCREEN"
>Section "Module"
    Load "v4l"
EndSection</PRE
></P
><P
>As of XFree86 4.2 this driver still supports only V4L
ioctls, however it should work just fine with all V4L2 devices through
the V4L2 backward-compatibility layer. Since V4L2 permits multiple
opens it is possible (if supported by the V4L2 driver) to capture
video while an X client requested video overlay. Restrictions of
simultaneous capturing and overlay are discussed in <A
HREF="x6570.htm"
>Section 4.2</A
> apply.</P
><P
>Only marginally related to V4L2, XFree86 extended Xv to
support hardware YUV to RGB conversion and scaling for faster video
playback, and added an interface to MPEG-2 decoding hardware. This API
is useful to display images captured with V4L2 devices.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN16446"
>6.3.2. Digital Video</A
></H2
><P
>V4L2 does not support digital terrestrial, cable or
satellite broadcast. A separate project aiming at digital receivers
exists. You can find its homepage at <A
HREF="http://linuxtv.org"
TARGET="_top"
>http://linuxtv.org</A
>. The Linux DVB API
has no connection to the V4L2 API except that drivers for hybrid
hardware may support both.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN16450"
>6.3.3. Audio Interfaces</A
></H2
><P
>[to do - OSS/ALSA]</P
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN16435"
HREF="x16430.htm#AEN16435"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>This is not implemented in XFree86.</P
></TD
></TR
></TABLE
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="x15446.htm"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="book1.htm"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="x16453.htm"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Changes of the V4L2 API</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="c14595.htm"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Experimental API Elements</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
